Note: Descriptions are shown in the official language in which they were submitted.
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COMPOSITE POLYMERS
FIELD OF THE INVENTION
'[0001] The present invention relates generally to the preparation of cosmetic
body panels having Class A Surface Quality from polymeric, low-density
composites.
BACKGROUND
[0002] The information provided below is not admitted to be prior art to the
present invention, but is provided solely to assist the understanding of the
reader.
[0003] With the continued increase in energy costs, the transportation
industry
has a strong desire to reduce the weight of their vehicles to improve fuel
economy. This
need to produce lighter vehicle parts has opened the door for the use of low
density
metals and polymers. Polymeric materials are now being used extensively to
replace
steel parts on vehicles due to their light weight, ability to be molded into
complex
shapes, i.e. part consolidation and design flexibility, corrosion resistance,
strength, and
resistance to damage. In particular, therrnoset composites are widely used to
prepare
structural (inner) and cosmetic (outer) body panels. The automotive industry
has very
stringent requirements for the surface appearance of cosmetic body panels. The
desired
smooth surface is generally referred to as a "Class A" surface. Surface
quality (SQ) as
measured by the Laser Optical Reflected Image Analyzer (LORIA), is determined
by
three measurements - Ashland Index (AI), Distinctness of Image (DOI), and
Orange
Pee (OP). SMC with Class A SQ is typically defined as having an Al <80, a DOI
> 70
(scale 0-100), and an OP > 7.0 (scale 0-10).
[0004] Nearly all thermoset polymers show shrinkage, on a volume basis, as
they are cured. In a fiber reinforced polymer thermoset composite (FRP), this
results in
a very uneven surface because the reinforcing fibers cause peaks and valleys
when the
resin shrinks around them. A variety of methods have been used to help
thermoset
composites meet the stringent surface smoothness requirements for a class A
surface
and enabling the formulation of composites that meet or exceed the smoothness
of the
metal parts, which were typically used in these applications.
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[0005] A common method used to reduce cure shrinkage and improve surface
smoothness is to incorporate large amounts of inorganic fillers, such as
calcium
carbonate (CaCO3), into the composite's' formulation. Typically, the filler
content of the
formulation will be about equal to that of the resin on a volume basis. Thus,
filler
addition reduces the cure shrinkage of the overall composition simply because
there is
significantly less polymeric material to undergo shrinkage.
[0006] With the increasing pressure in the industry to improve gas mileage,
manufacturers are working harder and harder to reduce the weight of their
vehicles.
While FRPs have an advantage over most competitive materials because of lower
specific gravity, the high density of the inorganic fillers and fiber
reinforcement,
typically glass, causes the part to be heavier than necessary. Most inorganic
fillers and
fiber reinforcement have a high density compared to polymeric thermoset
resins. For
example, calcium carbonate and glass fiber, the most commonly used filler and
reinforcement, both have a density of about 2.7 g/cc. Even though a typical
cured
thermoset, such as cured unsaturated polyester, has a density of about 1.2
g/cc, the filler
and glass fiber increase the density of a FRP body panel to about 1.9 g/cc.
Reducing the
density of these parts by 15 to 25%, while maintaining the other desirable
properties of
the FRP, could result in significant weight savings for the vehicle.
[0007] The industry has expressed a need for low-density composite molding
compounds yielding parts having Class A Surface Quality. Some suppliers have
attempted to reduce the part density by replacing a portion of the heavy
inorganic fillers
with hollow glass microspheres. While this technique significantly reduces
density
without a substantial drop in SQ, molded cosmetic panels made in this way show
substantial reduction in the mechanical properties and matrix toughness shown
by the
present high-density molding compounds that are unacceptable to the industry.
To
make this situation worse, the use glass microspheres increases the number of
parts
flawed by "paint popping" at a time when a number of newly introduced, high-
density
systems are yielding parts showing a significant reduction in such flaws.
[0008] While maintaining Class A SQ and other desired properties as part
density is reduced appears more and more difficult, the following disclosure
will show
that cosmetic molded parts having a 15 to 25% drop in density can be
accomplished
without microspheres and with little or no loss in SO, mechanicals, matrix
toughness or
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resistance to "paint popping".
SUMMARY OF THE INVENTION
[0009] The present invention addresses the unmet needs of the prior art by
providing strong, tough, low-density molded composite parts having Class A SQ
and
density not greater than about 1.6 grams/cubic centimeter without to use of
glass
microspheres. It provides these properties by use of a molded fiber reinforced
composite formulated with dramatically reduced levels of standard filler types
such as
nanoclay, diatomaceous earth, mica, wollastonite (CaSiO3;), kaolin clay,
graphite,
ground carbon fiber, cellulose-based fillers, and similar materials.
[0010] An aspect of the present invention provides low-density moldings
having an average linear shrinkage, compared to the mold, of about -0.02 to
+0.1 5
percent and a' Class A" surface. The surface quality (SQ), as measured by the
Laser
Optical Reflected Image Analyzer (LORIA), is determined by three measurements
Ashland Index (AI), Distinctness of Image (DOI), and Orange Peel (OP). For the
purpose of this invention, moldings are defined as having a Class A SQ when
possessing an Al <85, a DOI _ 70 (scale 0-100), and an OP > 7.0 (scale 0-10).
[0011] An aspect of the present invention provides reinforced composite panels
having a density below 1.6 grams/cubic centimeter. According to a further
aspect, the
panels do not contain either filled or hollow glass microspheres.
[0012] According to yet a further aspect, the panels are formed from a
thermoset molding compound, which, when molded into a flat panel without
reinforcement, has an average linear cure shrinkage, when compared to the cold
mold,
of -0.1 to -0.2 percent.
[0013] According to yet a further aspect, the panels are formed from a
thermoset molding compound, which, when molded into a flat panel with
reinforcement, has an average linear cure shririkage, when compared to the
cold mold,
of -0.02 to +0.15 percent.
[0014] According to yet a further aspect, the panels are formed from a
thermoset molding compound, which, when molded, with reinforcement, into a
flat
panel approximately 0.1 inch (2.54 millimeters) thick on a highly polished
mold, has a
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surface smoothness, as defined by the Ashland Index (AI), Distinctness of
Image
(DOI), and Orange Peel (OP) values measured by a Laser Optical Reflected Image
Analyzer (LORIA), of Al <85, DOI _ 70 (scale 0-100), and OP > 7.0 (scale 0-
10).
[0015] Still other aspects and advantages of the present invention will become
readily apparent by those skilled in the art from the following detailed
description,
wherein it is shown and described preferred embodiments of the invention
simply by
way of illustration of the best mode contemplated of carrying out the
invention. For
considerations of convenience, the invention is described in terms of
reinforced
composite body panels for transportation vehicles. However, the invention is
not
limited to either body panels or to transportation vehicles. As will be
realized the
invention is capable of other and different embodiments, and its several
details are
capable of modifications in various obvious respects, without departin9 from
the
invention. Accordingly, the description is to be regarded as illustrative in
nature and not
as restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The invention is best understood from the following detailed
description
when read in connection with the accompanying drawing. Included in the drawing
are
the following figure:
[0017] Figure 1 is a table describing the impact of various filler(s) on
Surface
Quality of parts molded at 300 F from the inventive low density formulations.
[0018] It is to be noted, however, that the appended drawing illustrates only
typical embodiments of this invention and are therefore not to be considered
limiting of
its scope, for the invention may admit to other equally effective embodiments.
DETAILED DESCRIPTION OP THE PREFERRED EMBODIMENT
[0019] Standard composite parts from thermosetting polymers are used
extensively in the transportation industry. Typical such composite
formulations contain
high concentrations higher density inorganic fillers, i.e. CaCO3 filler at
levels > 180
parts per 100 parts of organic resins, to help reduce the cure shrinkage of
the
formulation. These high filler levels, coupled with the fiber reinforcement,
produced
molded composite panels having a much higher density, i.e. > 1.9
grams/centimeter3
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(g/cc), than their polymeric components' density of about 1.2
grams/centimeter3 (g/cc).
[0020] At present there is a strong demand for tough, lower density composite
cosmetic parts (specific gravity < 1.6 g/cc) with Class A surface quality in
the
transportation industry. However, due to industry mechanical and thermal
requirements, most composite molding compounds are formulated from various
polymeric thermosetting resins that typically show significant shrinkage
during cure.
This 'cure shrinkage" can result in molded composites having a very rough
surface due
to the resin shrinking around the fiber reinforcement. Current techniques to
reduce
shrinkage typically include the use of large amounts of higher density
fillers, such as
calcium carbonate and clay to produce cosmetic composite moldings having both
good
strength and smooth surface appearance. Unfortunately, these formulations
often
contain > 70 weight percent higher density filler and fiber reinforcement and
have a
density>_ 1.9 g/cm3.
[0021] The steady increase in fuel prices and need to reduce the generation of
"green house gases", i.e. carbon dioxide (CO2), make the improved energy
efficiency
seen from lighter vehicles utilizing lower density composite parts highly
desirable.
However, the weight savings realized with such lower density parts is of no
use if the
high strength, toughness (i.e. crack and 'paint pop' resistance), or good
surface
appearance typically found in higher density Class A composites is lost. For
example, it
is well known that replacing a portion of the high density fillers with hollow
glass
microspheres can significantly reduce density while maintaining SQ. However,
glass
microspheres are unacceptable in Class A cosmetic applications as they reduce
the
composite's strength, toughness, and "paint pop" resistance and make the
repair of
painting flaws nearly impossible.
[0022] It is also well known that the mechanical properties of thermoset
composite moldings are highly dependent on the level and type of its fiber
reinforcement. Since maintaining the required strength and toughness leaves
little
flexibility to adjust the level and type of fiber reinforcement, formulating
acceptable
lower density cosmetic composites appears dependent on dramatically reducing
the
filler level without significantly changing its desired properties. Evaluation
of Lower
density formulations has shown that simply reducing the level of CaCO3; used
in
standard systems will not yield an acceptable low density Class A molded part.
Rather,
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complete reformulation of the resin and replacement of the CaCO3 with a blend
of high
surface area fillers is required to achieve the above objectives.
[0023] A preferred methodology for the determination of surface quality is by
use of a Laser Optical Reflected Image Analyzer, i.e. LORIA as disclosed by
Hupp
(LJS4,853,777), the entire content of which is specifically incorporated by
reference for
all purposes. Surface quality (SQ), as measured by LORIA, is determined by
three
measurements -Ashland Index (AI), Distinctness of Image (DOI), and Orange Peel
(OP). SMC with Class A SQ is typically defined as having an AI < 85, a DOI >
70
(scale 0-100), and an OP_ 7.0 (scale 0-10).
[0024] An example of a conventional "toughened" thermoset composite
moiding formulation could have the following approximate composition: 39g of a
highly reactive, toughened unsaturated polyester (UPE) resin; 14g of
thermoplastic low
profile additive (LPA), 3-4g of thermoplastic rubber impact modifier; 40-45g
of
reactive vinyl monomer, i.e. styrene monomer; 190-200g of CaCO3 filler; 9- lOg
of
magnesium oxide thickener; 4-5g mold release; 1.5g tertiary butyl perbenzoate
free-
radical initiator; and 0.05g of an "activator", i.e. cobalt, to speed up the
generation of
free-radicals by said initiator. Such conventional molding formulations
typically have a
density of > 1 .9g/cc.
[0025] The present invention is designed to provide a molding formulation to
mold cosmetic parts having a density of from 1.45 to 1.6g/cc while maintaining
the
mechanical properties, toughness, paint pop resistance, and Class A SQ of
higher
density parts. A lower density, molding composition might be comprised of 38-
40g of a
highly reactive, toughened unsaturated polyester (UPE) resin; 14g of
thermoplastic low
profile additive (LPA), 3-4g of thermoplastic rubber impact modifier; 40-45g
of
reactive vinyl monomer, i.e. styrene monomer; 35-65g of mixed filler; 9-lOg of
magnesium oxide thickener; 4-5g mold release; 1.5-1 .7g of free-radical
initiator; and
0.05g of an "activator", i.e. cobalt, to speed up the generation of free-
radicals by said
initiator. The mixed filler might include filler types such as nanoclay
(organically
treated clays that delaminate into nanoplatelets when subjected to shear
during mixing),
diatomaceous earth, mica, wollastonite (CaSiO3), kaolin clay, graphite, ground
carbon
fiber, cellulose-based fillers and similar materials.
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[0026] A typical filler package for lower density molding compound might
include 1-6g of nanoclay, 0-20g of diatomaceous earth, 0 to 25g mica, 0 to 25g
wollastonite, and/or 0 to 60g of kaolin clay, CaCO3, graphite, ground carbon
fiber, or
cellulosic organic. Combinations of these fillers will typically total 35 to
65g per lOOg
of organic resins and reactive monomers. Filler levels at the high end of the
range tend
to yield better mechanical properties and SQ, however, they increase density
and can
increase the formulation viscosity and make preparation of the molding
compound
more difficult. The filled resin paste viscosity is typically kept between
15,000 and
35,000 cps to ensure proper 'wet-out' of the fiber reinforcement prior to
molding.
[0027] Sheet molding compound paste (SMC-paste) formulations and
reinforced, sheet molding compounds (SMC) suitable for purposes of the present
invention have been described in co-pending applications 11/124,356;
11/124,294; and
11/124,354, the contents of which are incorporated by reference in their
respective
entireties and for all purposes. SMC-paste formulations comprise at least one
thermosetting resin, as described in co-pending application 11/124,356; at
least one
ethylenically unsaturated monomer, as described in co-pending application
11/124,356;
at least one low profiling additive, as described in -co-pending application
11/124,356; a
nanoclay filler composition, as described in co-pending application
11/124,356. An
aspect of the present invention provides that the SMC-paste does not contain
either
filled or hollow glass microspheres. A further aspect of the invention
provides that the
SMC-paste has a density less than about 1.25 g/cm3.
[0028] In preferred aspects, the thermosetting resin is a toughened, high-
elongation unsaturated polyester resin as described in co-pending application
11/124,356. Preferred, but non-limiting toughened, high-elongation unsaturated
polyester resins comprise a polyethylene glycol maleate UPE modified with at
least one
substituent selected from the group consisting of aromatic dibasic acids,
aliphatic
dibasic acids, glycols having from 2 to 8 carbons, and mixtures thereof.
[0029] According to alternative preferred aspects, the thermosetting resin
comprises from about 10 mole percent to about 40 mole percent of a phthalate-
modified, maleic-glycol polyester resin and from about 60 mole percent to
about 90
mole percent of a maleic-glycol polyester resin as described in co-pending
application
11/124,354.
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[0030] According to preferred aspects, the SMG-paste formulations further
comprise an alternative reactive monomer consisting of an aromatic,
multiethylenically-unsaturated monomer as described in co-pending application
11/124,294. A preferred, but non-limiting, alternative reactive monomer is
divinylbenzene.
[0031] SMC-paste formulations suitable for purposes of the present invention
may further comprise a reinforcing mineral filler as described in co-pending
application
11/124,356. Preferred, but non limiting mineral fillers include mica,
wollastonite, and
mixtures thereof.
[0032] SMC-paste formulations suitable for purposes of the present invention
may further comprise an organic filler as described in co-pending application
11/1
24356. Preferred, but non-limiting organic fillers include graphite, ground
carbon fiber,
celluloses, polymers, and mixtures thereof.
[0033] Ethylenically unsaturated monomers suitable for purposes of the present
invention have been described in co-pending application 11/124,356. Suitable
ethylenically-unsaturated monomers include, but are not limited to: acrylates,
methacrylates, methyl methacrylate, 2-ethylhexyl acrylate, styrene divinyl
benzene and
substituted styrenes, multkfunctional acrylates, ethylene glycol
dimethacrylate,
trimethylol propanetriacrylate, and mixtures thereof. A preferred
ethylenically
unsaturated monomer is styrene.
[00341 Suitable low profiling additives are thermoplastic resins as described
in
co-pending application 11/1 24,356. Suitable low profiling thennoplastic
resins include,
but are not limited to saturated polyester, polyurethane, polyvinyl acetate,
polymethylmethacrylate, polystyrene, epoxy extended polyester, and mixtures
thereof.
[0035] The SMC-paste formulations may further comprise a LPA-enhancer as
described in co-pending application 11/124,356.
[0036] The SMC-paste formulations may further comprise a rubber impact
modifier as described in co-pending application 11/124,356.
[0037] The SMC-paste formulations may further comprise at least one auxiliary
component selected from the group consisting of mineral fillers, organic
fillers,
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auxiliary monomers, rubber impact modifiers, resin tougheners, organic
initiators,
stabilizers, inhibitor thickeners, cobalt promoters, nucleating agents,
lubricants,
plasticizers, chain extenders, colorants, mold release agents, antistatic
agents, pigments,
fire retardants, and mixtures thereof as described in co-pending application
11/1 24356.
[0038] Low-density sheet molding compounds (SMC) suitable for purposes of
the present invention have been described in co--pending applications
11/124,356;
11/124,294; and 11/124,354. Briefly, low-density sheet molding compounds
suitable
for purposes of the present invention comprise a fibrous roving material and
an SMC-
paste as described above. Suitable SMC have densities less than about 1.6
g/cm3. The
SMC of the present invention do not contain glass microspheres.
[0039] Aspects of the present invention provide articles of manufacture
comprising the low-density SMC and/or SMC-pastes as described above.
[0040] Aspects of the invention provide methods of fabricating an article of
manufacture. The inventive methods include at least heating under pressure the
low-
density SMC and/or SMC-pastes described above.
[0041 ] In an aspect, a method of fabricating a low-density SMC is provided.
The method comprises forming a nanoclay composite in situ within an uncured
resin -
monomer mixture and curing said mixture, wherein said 5MG molding has a
density
less than about 1.6 g/cm3.
[0042] Aspects of the invention also provide a process for making molded
composite vehicle and construction parts having a density less than 1.6 grams
per cm3.
The process comprises admixing an unsaturated polyester thermosetting resin,
an
olefinically unsaturated monomer capable of copolymerizing with the
unsaturated
polyester resin, a thermoplastic low profile additive, free radical initiator,
alkaline earth
oxide or hydroxide thickening agent, and a nanoclay composite filler
composition:
forming a paste;
dispensing said paste on a carrier film above and below a bed of roving,
forming a
molding sheet; enveloping the sheet in the carrier film; consolidating the
sheet;
maturing the sheet until a matured molding viscosity of 3 million to 70
million
centipoise is attained and the sheet is non-tacky, releasing the sheet from
the carrier
film; compression molding the sheet into a part in a heated mold under
pressure
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whereby a uniform flow of resin, filler, and glass occurs outward to the edges
of the
part; and removing the molded part.
[0043] In preferred aspects of the process, parts are formed by molding under
a
pressure of from 200 psi to 1400 psi and more preferably from 400 psi to 800
psi. In
preferred aspects of the process, parts are formed by molding at a temperature
of from
250 F to 315 F, more preferably from 270 F to 290 F, and most preferably from
275 F
to 285 F.
[0044] According to the method, SMC-paste and/or SMC formulations are
provided onto the surface of a highly-polished mold and formed under heat and
pressure into a flat panel approximately 0.1 inch (2.54 millimeters) thick.
The SMC-
paste and/or SMC formulations do not contain glass microspheres. The resulting
panel
has a surface smoothness, as defined by the Ashland Index (AI), Distinctness
of Image
(DOI), and Orange Peel (OP) values measured by a Laser Optical Reflected Image
Analyzer (LORIA), of Al <85, DOI >_ 70 (scale 0-100), and OP > 7.0 (scale 0-
10).
Preferably, the molded part has a surface smoothness quality less than a 75
Ashland
LORIA analyzer index. The surface smoothness is a function of the mold surface
into
which the SMC-paste is pressed. In the above definition, a highly-polished
mold refers
to a mold that has been polished to a mirror finish. As understood in the
industry, a
mirror finish refers to a"#8 Finish," the most reflective finish commonly
produced on
sheet, also known as mirror or polished. It is produced by polishing with
successively
finer abrasives, then buffing with a very fine buffing compounds or rouges.
The surface
is essentially free of grit lines from preliminary grinding operations,
though, at certain
angles, some may still be visible.
[0045] The invention is illustrated with one example. Resin paste formulations
without reinforcement were cured and evaluated for "linear shrinkage" with the
best
being mixed with fiber reinforcement and molded into flat, 12 inch by 12 inch
reinforced panels about 0.1 inches thick. The panels were tested for density,
surface
appearance, and mechanical strength. The surface appearance was analyzed using
a
LORIA surface analyzer to measure the Ashland Index for 'long term waviness'
and
the Distinctness of Image (DOI) and Orange Peel (OP) for 'short term' surface
distortion.
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[0046] The data in Table I shows the formulations containing nanoclay plus
lowered filler level required to yield lower density, 1.5 - 1.6 g/cc, molded
panels. Note
the excellent overall SQ of the control (-1.9 g/cc). The data for formulations
TLM-1
through TLM-8 clearly show that obtaining a lower density SMC with acceptable
SQ is
not simply a matter of reducing the CaCO3 level. In fact, they show the
necessity of
employing a mixture of fillers having differing shapes and surface area to
prepare an
acceptable molded panel. The data also show that a correct mix of fillers is
key. Note
that TLM-5 and TLM-7, which contain CaC03i show significantly more shrinkage
and
reduced SQ compared to TLM-6 and TLM-8 where clay is the third filler
component.
[0047] It should be noted that cure shrinkage can be significantly reduced by
using higher levels of highly structured fillers such as nanoclay,
wollastonite, mica, and
diatomaceous earth. However, increased levels of such fillers cause a large
increase in
the viscosity of the resin paste and gives poor fiber 'wet-out' when preparing
reinforced
molding compound. Poor fiber 'wet-out' causes a multitude of problems when the
part
is molded, including poor SQ, reduced physical properties, delamination, and
'blistering'.
INCORPORATION BY REFERENCE
[0048] All publications, patents, and pre-grant patent application
publications
cited in this specification are herein incorporated by reference, and for any
and all
purposes, as if each individual publication or patent application were
specifically and
individually indicated to be incorporated by reference. In particular co-
pending
applications 11/124,356:11/124,294; and 11/124,354 are specifically
incorporated by
reference. In the case of inconsistencies the present disclosure will prevail.
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